QT学习笔记QserialPort类学习（一）

这篇博客记录一下QSerialPort类的学习成果，虽然用过多次了，但是从来没有仔细查看过官方的说明，所以这篇博客主要参考QT官方文档，给自己一个明确的，详细的使用方法，或许会发现点意外收获也说不定。

1、概述

QSerialPort类提供的是是一个接入串口的功能，它从QT的5.1版本之后才开始有，它继承自QIODevice。还有一个串口辅助的类QSerialPortInfo，它可以列举出系统里所有的串口，通过这个类，配合setPort和setPortName方法，我们就可以安排一下自己想用的串口了。下面是这类需要的头文件和工程文件的添加的qmake语句：

Header:	#include
qmake:	QT += serialport

官方文档上提到一个“All functions in this class are reentrant.”这个类里面所有的函数都是可重入的。这里的可重入意思是允许被递归调用的函数。这就意味着，这个类的函数正被调用尚未返回时，也可以直接或间接调用函数本身。一般的函数不能做到这样，只有重入函数才允许递归调用。

2、类中包含的公用类型

enum	BaudRate { Baud1200, Baud2400, Baud4800, Baud9600, ..., UnknownBaud }
enum	DataBits { Data5, Data6, Data7, Data8, UnknownDataBits }
enum	Direction { Input, Output, AllDirections }
flags	Directions
enum	FlowControl { NoFlowControl, HardwareControl, SoftwareControl, UnknownFlowControl }
enum	Parity { NoParity, EvenParity, OddParity, SpaceParity, MarkParity, UnknownParity }
enum	PinoutSignal { NoSignal, TransmittedDataSignal, ReceivedDataSignal, DataTerminalReadySignal, ..., SecondaryReceivedDataSignal }
flags	PinoutSignals
enum	SerialPortError { NoError, DeviceNotFoundError, PermissionError, OpenError, ..., UnknownError }
enum	StopBits { OneStop, OneAndHalfStop, TwoStop, UnknownStopBits }

 3、参数相关

*1、baudRate : qint32

这是设置串口波特率的。此项设置需要在串口打开之前，否则会回设置失败，返回一个错误，这个返回的错误值可以在QSerialPort::error里面看到。设置成功，返回一个true，然后在QSerialPort::open()运行的时候自动加载配置。要是想设置波特率，那就可以通过QSerialPort::BaudRate的枚举或者直接写一个qint32类型的数据。这个波特率的默认值是9600，也就是9600bits每秒。

跟这个参数相关的函数有这两个：

qint32	baudRate(Directions directions = AllDirections) const
bool	setBaudRate(qint32 baudRate, Directions directions = AllDirections)

相关的信号呢？

void	baudRateChanged(qint32 baudRate, QSerialPort::Directions directions)

*2、flowControl : FlowControl

这个是设置串口的流控的。跟波特率一样，要在打开串口之前设置。也可以在QSerialPort::error里面看到错误反馈。流控的默认配置是关闭的，默认值为NoFlowControl。

跟这个参数相关的函数有这两个：

FlowControl	flowControl() const
bool	setFlowControl(FlowControl flowControl)

相关的信号有：

void	flowControlChanged(QSerialPort::FlowControl flow)

*3、parity : Parity

这个参数是设置校验方式的，跟波特率一样，要在打开串口之前设置。默认是没有校验的，值是NoParity。

跟这个参数相关的函数有这两个：

Parity	parity() const
bool	setParity(Parity parity)

相关信号有：

void	parityChanged(QSerialPort::Parity parity)

*4、dataBits : DataBits

控制数据位的，设置方法跟波特率差不多，也是在串口打开之前设置。默认是8数据位，值是Data8。

跟这个参数相关的函数有两个：

DataBits	dataBits() const
bool	setDataBits(DataBits dataBits)

相关信号有：

void	dataBitsChanged(QSerialPort::DataBits dataBits)

*4、stopBits : StopBits

控制停止位的，设置方法同上。默认是1停止位，值是OneStop。

相关的函数有：

StopBits	stopBits() const
bool	setStopBits(StopBits stopBits)

相关信号有：

void	stopBitsChanged(QSerialPort::StopBits stopBits)

*5、breakEnabled : bool

这个参数是设置传送状态的。如果返回true，那传送线路就是切断状态，否则就是非切断状态。这个参数的设置或者查询必须在串口打开之后，如果串口没打开，设置这个参数会报NotOpenError。这个参数不常用。

相关的函数：

bool	isBreakEnabled() const
bool	setBreakEnabled(bool set = true)

相关的信号：

void	breakEnabledChanged(bool set)

*6、dataTerminalReady : bool

数据终端就绪的参数，会保持一个状态（高或者低）。返回值是true代表成功，false代表失败。如果标志位是true，说明DTR（dataTerminalReady）信号被设置为高了，反之说明是低。设置或者查询这个参数的前提是串口已经打开了，否则会也会报NotOpenError的错误。

相关函数：

bool	isDataTerminalReady()
bool	setDataTerminalReady(bool set)

相关信号：

void	dataTerminalReadyChanged(bool set)

*7、error : SerialPortError

这个参数会记录串口的错误状态。I/O设备的状态出错时会返回错误码。这个参数可以用来查找错误原因。如果clearError()函数被调用了，那么错误码就会被设置为默认状态，也就是QSerialPort::NoError。

相关的函数有：

SerialPortError	error() const
void	clearError()

*8、requestToSend : bool

请求发送的参数。这个参数跟dataTerminalReady类似，也是保持一个高或者低的状态。设置成功则返回true，否则返回false。如果标志位是true，RTS（requestToSend）就是高，反之则是低。这里注意一点：如果在HardwareControl模式下，发送RTS信号会失败，错误提示是UnsupportedOperationError，这是因为此时的信号是由驱动自动控制的。

相关的函数：

bool	isRequestToSend()
bool	setRequestToSend(bool set)

相关的信号：

void	requestToSendChanged(bool set)

4、成员类型记录

*1、enum QSerialPort::BaudRate

下面的枚举是描述设备通信波特率的。这里只列出了一些比较常用的。

Constant	Value	Description
QSerialPort::Baud1200	1200	1200 baud.
QSerialPort::Baud2400	2400	2400 baud.
QSerialPort::Baud4800	4800	4800 baud.
QSerialPort::Baud9600	9600	9600 baud.
QSerialPort::Baud19200	19200	19200 baud.
QSerialPort::Baud38400	38400	38400 baud.
QSerialPort::Baud57600	57600	57600 baud.
QSerialPort::Baud115200	115200	115200 baud.
QSerialPort::UnknownBaud	-1	Unknown baud. 已经废弃，新版本不要用。

*2、enum QSerialPort::DataBits

下面的枚举是用来描述数据位的。

Constant	Value	Description
QSerialPort::Data5	5	The number of data bits in each character is 5. It is used for Baudot code. It generally only makes sense with older equipment such as teleprinters.
QSerialPort::Data6	6	The number of data bits in each character is 6. It is rarely used.
QSerialPort::Data7	7	The number of data bits in each character is 7. It is used for true ASCII. It generally only makes sense with older equipment such as teleprinters.
QSerialPort::Data8	8	The number of data bits in each character is 8. It is used for most kinds of data, as this size matches the size of a byte. It is almost universally used in newer applications.
QSerialPort::UnknownDataBits	-1	Unknown number of bits. This value is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.

*3、enum QSerialPort::Direction 和 flags QSerialPort::Directions

这里的枚举代表数据传输的方向，某些操作系统里设置波特率的时候它可以区分不同方向的波特率。（像OPSIX-like）

Constant	Value	Description
QSerialPort::Input	1	Input direction.
QSerialPort::Output	2	Output direction.
QSerialPort::AllDirections	Input | Output	Simultaneously in two directions.

方向的类型是QFlags类型的typedef。它存储了这两种方向值通过“或”的组合。

*4、enum QSerialPort::FlowControl

这个枚举是对流控的描述。

Constant	Value	Description
QSerialPort::NoFlowControl	0	No flow control.
QSerialPort::HardwareControl	1	Hardware flow control (RTS/CTS).
QSerialPort::SoftwareControl	2	Software flow control (XON/XOFF).
QSerialPort::UnknownFlowControl	-1	Unknown flow control. This value is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.

*5、enum QSerialPort::Parity

这个枚举是校验方案的描述。

Constant	Value	Description
QSerialPort::NoParity	0	No parity bit it sent. This is the most common parity setting. Error detection is handled by the communication protocol.
QSerialPort::EvenParity	2	The number of 1 bits in each character, including the parity bit, is always even.
QSerialPort::OddParity	3	The number of 1 bits in each character, including the parity bit, is always odd. It ensures that at least one state transition occurs in each character.
QSerialPort::SpaceParity	4	Space parity. The parity bit is sent in the space signal condition. It does not provide error detection information.
QSerialPort::MarkParity	5	Mark parity. The parity bit is always set to the mark signal condition (logical 1). It does not provide error detection information.
QSerialPort::UnknownParity	-1	Unknown parity. This value is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.

*6、enum QSerialPort::PinoutSignal 和 flags QSerialPort::PinoutSignals

这个枚举描述了RS-232引脚输出信号的可能情况。

Constant	Value	Description
QSerialPort::NoSignal	0x00	No line active
QSerialPort::TransmittedDataSignal	0x01	TxD (Transmitted Data). This value is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.
QSerialPort::ReceivedDataSignal	0x02	RxD (Received Data). This value is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.
QSerialPort::DataTerminalReadySignal	0x04	DTR (Data Terminal Ready).
QSerialPort::DataCarrierDetectSignal	0x08	DCD (Data Carrier Detect).
QSerialPort::DataSetReadySignal	0x10	DSR (Data Set Ready).
QSerialPort::RingIndicatorSignal	0x20	RNG (Ring Indicator).
QSerialPort::RequestToSendSignal	0x40	RTS (Request To Send).
QSerialPort::ClearToSendSignal	0x80	CTS (Clear To Send).
QSerialPort::SecondaryTransmittedDataSignal	0x100	STD (Secondary Transmitted Data).
QSerialPort::SecondaryReceivedDataSignal	0x200	SRD (Secondary Received Data).

这里的引脚输出信号类型是QFlags的Typedef。它保存了这些引脚输出信号值“或”的组合。

*7、enum QSerialPort::SerialPortError

这个枚举描述了QSerialPort::error参数可能包含的错误情况。

Constant	Value	Description
QSerialPort::NoError	0	No error occurred.
QSerialPort::DeviceNotFoundError	1	An error occurred while attempting to open an non-existing device.
QSerialPort::PermissionError	2	An error occurred while attempting to open an already opened device by another process or a user not having enough permission and credentials to open.
QSerialPort::OpenError	3	An error occurred while attempting to open an already opened device in this object.
QSerialPort::NotOpenError	13	This error occurs when an operation is executed that can only be successfully performed if the device is open. This value was introduced in QtSerialPort 5.2.
QSerialPort::ParityError	4	Parity error detected by the hardware while reading data. This value is obsolete. We strongly advise against using it in new code.
QSerialPort::FramingError	5	Framing error detected by the hardware while reading data. This value is obsolete. We strongly advise against using it in new code.
QSerialPort::BreakConditionError	6	Break condition detected by the hardware on the input line. This value is obsolete. We strongly advise against using it in new code.
QSerialPort::WriteError	7	An I/O error occurred while writing the data.
QSerialPort::ReadError	8	An I/O error occurred while reading the data.
QSerialPort::ResourceError	9	An I/O error occurred when a resource becomes unavailable, e.g. when the device is unexpectedly removed from the system.
QSerialPort::UnsupportedOperationError	10	The requested device operation is not supported or prohibited by the running operating system.
QSerialPort::TimeoutError	12	A timeout error occurred. This value was introduced in QtSerialPort 5.2.
QSerialPort::UnknownError	11	An unidentified error occurred.

*8、enum QSerialPort::StopBits

这个枚举描述的是停止位的数量。

Constant	Value	Description
QSerialPort::OneStop	1	1 stop bit.
QSerialPort::OneAndHalfStop	3	1.5 stop bits. This is only for the Windows platform.
QSerialPort::TwoStop	2	2 stop bits.
QSerialPort::UnknownStopBits	-1	Unknown number of stop bits. This value is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.

下一篇要总结一下QSerialPort类的成员函数。这一篇先写这么多。